Re: [RFC PATCH 3/4] dt-bindings: panel: Introduce dual-link LVDS panel

[Aradhya Bhatia]

Hi Krzysztof,

Thank you for reviewing the patches!

On 03-Jan-23 14:02, Krzysztof Kozlowski wrote:
> On 03/01/2023 07:46, Aradhya Bhatia wrote:
> > Dual-link LVDS interfaces have 2 links, with even pixels traveling on
> > one link, and odd pixels on the other. These panels are also generic in
> > nature, with no documented constraints, much like their single-link
> > counterparts, "panel-lvds".
> >
> > Add a new compatible, "panel-dual-lvds", and a dt-binding document for
> > these panels.
> >
> > Signed-off-by: Aradhya Bhatia <a-bhatia1@xxxxxx>
> > ---
> >   .../display/panel/panel-dual-lvds.yaml        | 157 ++++++++++++++++++
> >   MAINTAINERS                                   |   1 +
> >   2 files changed, 158 insertions(+)
> >   create mode 100644 Documentation/devicetree/bindings/display/panel/panel-dual-lvds.yaml
> >
> > diff --git a/Documentation/devicetree/bindings/display/panel/panel-dual-lvds.yaml b/Documentation/devicetree/bindings/display/panel/panel-dual-lvds.yaml
> > new file mode 100644
> > index 000000000000..88a7aa2410be
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/display/panel/panel-dual-lvds.yaml
> > @@ -0,0 +1,157 @@
> > +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> > +%YAML 1.2
> > +---
> > +$id: http://devicetree.org/schemas/display/panel/panel-dual-lvds.yaml#
> > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > +
> > +title: Generic Dual-Link LVDS Display Panel
> > +
> > +maintainers:
> > +  - Aradhya Bhatia <a-bhatia1@xxxxxx>
> > +  - Thierry Reding <thierry.reding@xxxxxxxxx>
> > +
> > +description: |
> > +  A dual-LVDS interface is a dual-link connection with the even pixels
> > +  traveling on one link, and the odd pixels traveling on the other.
> > +
> > +allOf:
> > +  - $ref: panel-common.yaml#
> > +  - $ref: /schemas/display/lvds.yaml/#
>
> Drop trailing /

Okay, will do!

> > +
> > +properties:
> > +  compatible:
> > +    oneOf:
> > +      - items:
> > +          - enum:
> > +              - lincolntech,lcd185-101ct
> > +              - microtips,13-101hieb0hf0-s
> > +          - const: panel-dual-lvds
> > +      - const: panel-dual-lvds
>
> You cannot have this compatible alone
Okay, will make the change!

> > +
> > +  ports:
> > +    $ref: /schemas/graph.yaml#/properties/ports
> > +
> > +    properties:
> > +      port@0:
> > +        $ref: /schemas/graph.yaml#/$defs/port-base
> > +        unevaluatedProperties: false
> > +        description: The sink for first set of LVDS pixels.
> > +
> > +        properties:
> > +          dual-lvds-odd-pixels:
> > +            type: boolean
> > +
> > +          dual-lvds-even-pixels:
> > +            type: boolean
> > +
> > +        oneOf:
> > +          - required: [dual-lvds-odd-pixels]
> > +          - required: [dual-lvds-even-pixels]
> > +
> > +      port@1:
> > +        $ref: /schemas/graph.yaml#/$defs/port-base
> > +        unevaluatedProperties: false
> > +        description: The sink for second set of LVDS pixels.
> > +
> > +        properties:
> > +          dual-lvds-even-pixels:
> > +            type: boolean
> > +
> > +          dual-lvds-odd-pixels:
> > +            type: boolean
> > +
> > +        oneOf:
> > +          - required: [dual-lvds-even-pixels]
> > +          - required: [dual-lvds-odd-pixels]
> > +
> > +    allOf:
> > +      - if:
> > +          properties:
> > +            port@0:
> > +              properties:
> > +                dual-lvds-odd-pixels: true
>
> That's not correct clause. It has no effect.

The idea behind this is to check the presence of the boolean property.

if (dual-lvds-odd-pixels is present)
then
[..]


I tried implementing this:

	[..]
	  dual-lvds-odd-pixels:
	    - const: true
	[..]

But this is throwing an error. I am confused what else could be done.
Can you please suggest what might be a more accurate check here?

> > +              required:
> > +                - dual-lvds-odd-pixels
> > +        then:
> > +          properties:
> > +            port@1:
> > +              properties:
> > +                dual-lvds-even-pixels: true
> > +                dual-lvds-odd-pixels: false
>
> Why do you need this? Your oneOf before already solves it.

I agree with your comment here. It makes sense to only have

	dual-lvds-even-pixels: true

and have the oneOf condition take care of the other. But, I just tested
this and it was unable to pick-up this intentionally-added error.

I added 'dual-lvds-odd-pixels' property to both the nodes, and
dt_binding_check passes successfully (which it should have not.)

Instead, if I only keep this,

	dual-lvds-odd-pixels: false

then the dt_binding_check detects the error as it should.

Regardless, I am curious why the first method doesn't work. Will try to
explore more on that.

> > +
> > +      - if:
> > +          properties:
> > +            port@0:
> > +              properties:
> > +                dual-lvds-even-pixels: true
> > +              required:
> > +                - dual-lvds-even-pixels
> > +        then:
> > +          properties:
> > +            port@1:
> > +              properties:
> > +                dual-lvds-odd-pixels: true
> > +                dual-lvds-even-pixels: false
> > +
> > +    required:
> > +      - port@0
> > +      - port@1
> > +
> > +  port: false
> > +
> > +unevaluatedProperties: false
> > +
> > +required:
> > +  - compatible
> > +  - width-mm
> > +  - height-mm
> > +  - data-mapping
> > +  - panel-timing
> > +  - ports
> > +
> > +examples:
> > +  - |+
>
> Drop +

Okay!

> > +    panel-dual-lvds {
>
> Just "panel". Node names should be generic.

Alright. Will make the change!

> > +      compatible = "microtips,13-101hieb0hf0-s", "panel-dual-lvds";
> > +
> > +      width-mm = <217>;
> > +      height-mm = <136>;
> > +
Regards
Aradhya